Highly dielectric film

ABSTRACT

There is provided a highly dielectric film which has high dielectric property, can be formed into a think film and is excellent in winding property (flexibility). The highly dielectric film comprises (A) a vinylidene fluoride polymer, (B) barium titanate oxide particles and/or lead zirconium titanate oxide particles, and (C) an affinity improving agent, wherein the barium titanate oxide particles and/or lead zirconium titanate oxide particles (B) and the affinity improving agent (C) are contained in amounts of 10 to 500 parts by mass and 0.01 to 30 parts by mass, respectively based on 100 parts by mass of the vinylidene fluoride polymer (A).

TECHNICAL FIELD

The present invention relates to a highly dielectric film being useful,for example, as a dielectric film for a film condenser.

BACKGROUND ART

In recently years, plastic insulating materials are expected as filmmaterials for film condensers for communication, electronic devices,electric power, medium and low voltage phase advancement and inverter,piezoelectric devices, pyroelectric devices and dielectric materials fortransfer printing carrier since they have a high insulation resistance,excellent frequency characteristics and excellent flexibility.

A film condenser is usually comprised of a film structure comprising adielectric polymer film subjected to aluminum or zinc deposition on itssurface, or a film structure comprising multi-layers of aluminum foilsand dielectric polymer films, and recently there are used a lot ofcondenser films comprising a dielectric polymer film and an electrodeformed thereon by metal deposition.

Hydrocarbon polymers such as polypropylene, polyester and polyphenylenesulfide are studied as a dielectric polymer for a film of filmcondenser. However a dielectric constant of such a film itself is onlyabout 2.3 to about 3.

It is known that a capacity of a film condenser is proportional to adielectric constant of a film and reversely proportional to a filmthickness.

Therefore, making a film thinner has been studied, but if a film is madetoo thin, film formation becomes difficult, and lowering of a withstandvoltage is recognized. Accordingly there is a limit in making a filmthinner.

For making a dielectric constant of a film itself higher, highlydielectric polyvinylidene fluoride polymer and cyano-ethylated pullulanhave been studied as a polymer. However dielectric constants of any ofthese films are not more than 20, and those polymers are materialsmaking it difficult to make a film thinner.

In recent years, making a size of a film condenser smaller and itscapacity larger has been advanced, and as a result, it is stronglydemanded to make a dielectric constant higher.

As one of means for making a dielectric constant of a film condenserhigher, it is proposed to incorporate inorganic particles having anespecially high dielectric constant with a polymer to make a film.

For mixing highly dielectric inorganic particles to a polymer and makinga film, there are known (1) a melt-kneading method and (2) a coatingmethod.

The melt-kneading method (1) is a method of kneading highly dielectricinorganic particles and a polymer at a temperature of not less than amelting temperature of the polymer, making the mixture into a film by amelt-extrusion method or an inflation method, and if necessary,subjecting the film to stretching treatment. In this method, there areknown use of a hydrocarbon polymer such as polyphenylene sulfide,polypropylene or polyester (JP2000-501549A and JP2000-294447A) and useof a vinylidene fluoride polymer (for example, JP59-43039A, JP60-185303Aand JP58-69252A). However in these methods, it is difficult to produce athin film having a high dielectric constant and few voids.

The coating method (2) is a method of producing a film by dissolving apolymer in a solvent, adding and mixing thereto highly dielectricinorganic particles to make a coating composition, and then forming afilm by a coating method.

In the coating method (2), there are known use of rigid hydrocarbonpolymers being excellent in heat resistance and mechanical strength suchas aromatic polyamide, aromatic polyimide and an epoxy resin(JP2001-106977A, JP1-248404A, JP4-160705A, JP2-206623A andJP2002-356619A) and use of a vinylidene fluoride polymer (JP54-129397A).

In the case of using a rigid hydrocarbon polymer, it is possible toproduce a thin film having a high mechanical strength but there is alarge effect of a dielectric constant of the polymer itself, therebylimiting improvement of a film dielectric constant, and a film becomeshard. Therefore, it cannot be said that such a film is suitable as afilm for a film condenser which is required to have excellent windingproperty (flexibility). A system obtained by adding and mixing highlydielectric inorganic particles to a thermosetting resin is very hard,and is used for embedded capacitor, making use of its property of beinghard.

In the case of using a vinylidene fluoride polymer, it is difficult toobtain a film in which highly dielectric inorganic particles arehomogeneously incorporated in a polymer, and further improvement inmaking a thin film and increasing a dielectric constant is required.

Further it is proposed to produce a sheet comprising highly incorporatedhighly dielectric inorganic particles by press-molding compositeparticles prepared by coating highly dielectric inorganic particles witha vinylidene fluoride polymer (JP61-224205A). However the film is asthick as 150 μm, and cannot be said to be suitable as a film for a filmcondenser which is required to have excellent winding property(flexibility).

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a highly dielectricfilm which has high dielectric property, can be made thin and isexcellent in winding property (flexibility).

Namely, the present invention relates to a highly dielectric filmcomprising:

(A) a vinylidene fluoride (VdF) polymer,(B) barium titanate oxide particles and/or lead zirconium titanate oxideparticles, and(C) an affinity improving agent,wherein the barium titanate oxide particles and/or lead zirconiumtitanate oxide particles (B) and the affinity improving agent (C) arecontained in amounts of 10 to 500 parts by mass and 0.01 to 30 parts bymass, respectively based on 100 parts by mass of the VdF polymer (A).

The present invention also relates to a coating composition for forminga highly dielectric film comprising:

(A) a vinylidene fluoride (VdF) polymer,(B) barium titanate oxide particles and/or lead zirconium titanate oxideparticles,(C) an affinity improving agent, and(D) a solvent,wherein the barium titanate oxide particles and/or lead zirconiumtitanate oxide particles (B) and the affinity improving agent (C) arecontained in amounts of 10 to 500 parts by mass and 0.01 to 30 parts bymass, respectively based on 100 parts by mass of the VdF polymer (A).

Further the present invention relates to a method of producing thehighly dielectric film of the present invention which is characterizedby subjecting the coating composition of present invention to coating ona substrate and drying.

The highly dielectric film of the present invention is especiallysuitable as a film for a film condenser.

BRIEF EXPLANATION OF THE DRAWINGS

[FIG. 1] A SEM photograph (magnification 1,000) of a film produced inExample 2.

[FIG. 2] A SEM photograph (magnification 10,000) of a film produced inExample 2.

[FIG. 3] A SEM photograph (magnification 1,000) of a film produced inExample 3.

[FIG. 4] A SEM photograph (magnification 10,000) of a film produced inExample 3.

[FIG. 5] A SEM photograph (magnification 1,000) of a film produced inExample 18.

[FIG. 6] A SEM photograph (magnification 10,000) of a film produced inExample 18.

[FIG. 7] A SEM photograph (magnification 1,000) of a film produced inComparative Example 3.

[FIG. 8] A SEM photograph (magnification 10,000) of a film produced inComparative Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

The highly dielectric film of present invention is one comprising:

(A) a VdF polymer,(B) barium titanate oxide particles and/or lead zirconium titanate oxideparticles, and(C) an affinity improving agent,wherein the barium titanate oxide particles and/or lead zirconiumtitanate oxide particles (B) and the affinity improving agent (C) arecontained in amounts of 10 to 500 parts by mass and 0.01 to 30 parts bymass, respectively based on 100 parts by mass of the VdF polymer (A).

The VdF polymer may be a homopolymer of VdF or may be a copolymercomprising VdF and other copolymerizable monomer. Also the VdF polymermay be a blend of a homopolymer of VdF and a VdF copolymer or may be ablend of VdF copolymers.

Examples of the other copolymerizable monomer are, for instance,fluorine-containing olefins such as tetrafluoroethylene (TFE),chlorotrifluoroethylene (CTFE), trifluoroethylene, monofluoroethylene,hexafluoropropylene (HFP) and perfluoro(alkyl vinyl ether) (PAVE); afluorine-containing acrylate and a fluorine-containing monomer havingfunctional group. Among these, HFP, TFE and CTFE are preferable from theviewpoint of satisfactory solubility in a solvent. A proportion of theVdF is not less than 50% by mole, preferably not less than 60% by mole,from the viewpoint of a high dielectric constant and high solubility ina solvent. In the case of a VdF/TFE copolymer, it is preferable that thecopolymer comprises 60 to 95% by mole of a VdF unit and 5 to 40% by moleof a TFE unit, especially preferably 70 to 90% by mole of a VdF unit and10 to 30% by mole of a TFE unit, since a withstand voltage becomes high.A dielectric constant (20° C., 1 kHz) of the VdF polymer is preferablynot less than 7, further not less than 7.5, from the viewpoint offurther increasing a dielectric constant of a film.

The barium titanate oxide particles and/or lead zirconium titanate oxide(PZT) particles (B) (hereinafter may be simply referred to as “specifictitanium oxide particles (B)”) are representative highly dielectricinorganic particles, and a dielectric constant thereof is not less than500. Especially barium titanate oxide particles are preferable sincethey have a high dielectric constant exceeding 1,500, and are easilyformed into fine particles.

An average particle size of the specific titanium oxide particles (B) ispreferably not more than 2 μm, especially preferably from 0.01 to 0.5μm, particularly preferably from about 0.01 μm to about 0.2 μm, from theviewpoint of excellent smoothness of a film surface and satisfactoryhomogeneous dispersibility.

An amount of the specific titanium oxide particles (B) is not less than10 parts by mass, preferably not less than 30 parts by mass, especiallypreferably not less than 50 parts by mass based on 100 parts by mass ofthe VdF polymer. When its amount is too small, an effect of improving adielectric constant of a film becomes smaller. An upper limit thereof is500 parts by mass. When the amount is too large, there occur problemswith strength of a film and film surface roughness. A preferable upperlimit is 400 parts by mass, further 300 parts by mass.

The affinity improving agent (C) is a component playing a role of notonly improving affinity of the VdF polymer (A) for the specific titaniumoxide particles (B) and dispersing the both homogeneously but alsostrongly bonding the specific titanium oxide particles (B) and the VdFpolymer (A) in the film. Without this component (C), voids are easilygenerated in the film, and a dielectric constant is decreased. Further,in the film forming composition explained infra, the component (C)functions to homogeneously disperse the specific titanium oxideparticles and the VdF polymer.

Examples of the effective affinity improving agent (C) are a couplingagent (C1), a surfactant (C2) and an epoxy group-containing compound(C3).

Examples of the coupling agent (C1) are, for instance, a titaniumcoupling agent, a silane coupling agent, a zirconium coupling agent anda zircoaluminate coupling agent.

Examples of the titanium coupling agent are, for instance, those ofmonoalkoxy type, chelate type and coordinate type, and especially fromthe viewpoint of satisfactory affinity for the specific titanium oxideparticles (B), monoalkoxy type and chelate type are preferable.

Examples of the silane coupling agent are, for instance, those of highmolecular weight type and low molecular weight type, and from theviewpoint of the number of functional groups, there aremonoalkoxysilane, dialkoxysilane, trialkoxysilane and Dipodalalkoxysilane. Especially from the viewpoint of satisfactory affinity forthe specific titanium oxide particles (B), alkoxysilanes of lowmolecular weight type are preferable.

Examples of the zirconium coupling agent are, for instance,monoalkoxyzirconium and trialkoxyzirconium.

Examples of the zircoaluminate coupling agent are, for instance,monoalkoxyzircoaluminate and trialkoxyzircoaluminate.

Examples of the surfactant (C2) are those of high molecular weight typeand low molecular weight type, and from the viewpoint of kind offunctional groups, there are a nonionic surfactant, an anionicsurfactant and a cationic surfactant. Those can be used, and surfactantsof high molecular weight type are preferable from the viewpoint ofsatisfactory thermal stability.

Examples of the nonionic surfactant are, for instance, polyetherderivatives, polyvinyl pyrrolidone derivatives and alcohol derivatives,and polyether derivatives are preferable especially from the viewpointof satisfactory affinity for the specific titanium oxide particles (B).

Examples of the anionic surfactant are, for instance, polymers havingmoiety of sulfonic acid, carboxylic acid or salt thereof, and especiallyfrom the viewpoint of satisfactory affinity for the VdF polymer (A),preferable are acrylic acid derivative polymers, methacrylic acidderivative polymers, and maleic anhydride copolymers.

Examples of the cationic surfactant are, for instance, amine compounds,compounds having a nitrogen-containing complex ring such as imidazoline,and halogenated salts thereof, and compounds having anitrogen-containing complex ring are preferable since they have lessproperty of attacking the VdF polymer (A). Examples of the salts areammonium salts having halogen anion such as alkyltrimethylammoniumchloride. From the viewpoint of a high dielectric constant, ammoniumsalts having halogen anion are preferable.

Examples of the epoxy group-containing compound (C3) are epoxy compoundsand glycidyl compounds, which may be low molecular weight compounds orhigh molecular weight compounds. Particularly preferable are lowmolecular weight compounds having one epoxy group from the viewpoint ofespecially satisfactory affinity for the VdF polymer (A). In the presentinvention, epoxy group-containing coupling agents (for example,epoxysilane) which are classified into a coupling agent are included inthe coupling agent (C1) but not in the epoxy group-containing compound(C3).

From the viewpoint of especially satisfactory affinity for the VdFpolymer (A), preferable examples of the epoxy group-containing compound(C3) are compounds represented by the formula (C3):

wherein R is hydrogen atom, a monovalent hydrocarbon group having 1 to10 carbon atoms which may have oxygen atom, nitrogen atom orcarbon-carbon double bond, or an aromatic ring which may have asubstituent; l is 0 or 1; m is 0 or 1; n is 0 or an integer of 1 to 10.

Examples thereof are:

and the like, which have a ketone group or an ester group.

An amount of the component (C) is not less than 0.01 part by mass,preferably not less than 0.1 part by mass, especially preferably notless than 1 part by mass based on 100 parts by mass of the VdF polymer.When its amount is too small, dispersing homogeneously becomesdifficult. An upper limit thereof is 30 parts by mass. When its amountis too large, there occurs a problem that a dielectric constant of anobtained film is decreased. A preferable upper limit is 25 parts bymass, further 20 parts by mass.

From the viewpoint of satisfactory affinity for the specific titaniumoxide particles (B), the coupling agent (C1) and the epoxygroup-containing compound (C3) are preferable as the component (C), andespecially titanium coupling agents and silane coupling agents arepreferable from the viewpoint of satisfactory affinity for both of theVdF polymer (A) and the specific titanium oxide particles (B).

In addition, the coupling agent (C1) and the epoxy group-containingcompound (C3) exhibit more satisfactory affinity improving action sincethey form a chemical bond with the specific titanium oxide particles (B)(having a reaction group).

The film of the present invention may contain, as optional components,other polymer and other highly dielectric inorganic particles and inaddition, additives such as various fillers such as a reinforcing fillerand an antistatic filler and an affinity improving agent.

Preferable examples of other polymer are polycarbonate (PC), polyester,polyethylene terephthalate (PET), polyethylene naphthalate (PEN),silicone resin, polyether, polyvinyl acetate, polyethylene, andpolypropylene for improving flexibility; poly(meth)acrylate, epoxyresin, polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyamide(PA), polyimide (PI), polyamide imide (PAI), polycarbonate, polystyreneand polybenzimidazole (PBI) for increasing strength; and odd numberpolyamide, cyano pullulan, and copper phthalocyanine polymer forsupplementing high dielectric property. These other polymers may beblended to an extent not to impair the object of the present invention.

In the present invention, combination use of other highly dielectricinorganic particles is not prohibited, and known highly dielectricinorganic particles may be blended. Examples of such other highlydielectric inorganic particles are, for instance, zinc titanate,strontium titanate, calcium titanate, magnesium titanate, lead titanate,titanium oxide, barium antimonite, magnesium antimonite, strontiumantimonite, calcium antimonite, lead antimonite, barium stannate,strontium stannate, and complex compounds, solid solutions and mixturesthereof. These other highly dielectric inorganic particles may beblended to an extent not to impair the object of the present invention.In addition, highly dielectric organic particles, for example, copperphthalocyanine tetramer may be blended to an extent not to impair theobject of the present invention.

Examples of a reinforcing filler are, for instance, particles and fibersof silicon carbide, silicon nitride, magnesium oxide, potassiumtitanate, glass, alumina, and boron compounds, and examples of anaffinity improving agent are, for instance, polyolefin modified withfunctional group, styrene-modified polyolefin, polystyrene modified withfunctional group, polyacrylate imide and cumyl phenol. These may beblended to an extent not to impair the object of the present invention.

The highly dielectric film of the present invention can be produced byeither of the above-mentioned melt-kneading method (1) and the coatingmethod (2). From the viewpoint of easy production and excellenthomogeneity of an obtained film, it is advantageous to produce by thecoating method (2).

In the case of producing a highly dielectric film by the coating method,first a coating composition is prepared. The coating composition of thepresent invention is a composition comprising:

(A) a VdF polymer,(B) barium titanate oxide particles and/or lead zirconium titanate oxideparticles,(C) an affinity improving agent, and(D) a solvent,wherein the barium titanate oxide particles and/or lead zirconiumtitanate oxide particles (B) and the affinity improving agent (C) arecontained in amounts of 10 to 500 parts by mass and 0.01 to 30 parts bymass, respectively based on 100 parts by mass of the VdF polymer (A).

With respect to examples and amounts of the VdF polymer (A), thespecific titanium oxide particles (B), the affinity improving agent (C)and other optional components, the above-mentioned explanations can beapplied.

It is preferable to adjust a viscosity of this composition to 0.01 to 3Pa·s with the solvent (D) since coatability is satisfactory and auniform and smooth film can be obtained. It is especially preferablethat the viscosity is not more than 1.5 Pa·s, from the viewpoint ofinhibiting roughening of its surface.

A form of the composition may be an emulsion (a solvent is water, etc.).In this case, since both of the VdF polymer and the component (B) are inthe form of particles, a particle-particle mixture system is formed andit is difficult to homogeneously disperse them. Therefore it ispreferable to prepare a solution of the VdF polymer (A) dissolved in anorganic solvent and disperse the component (B) in that solution of theVdF polymer because the particles are easily dispersed homogeneously anda homogeneous film can be easily obtained.

Preferable examples of the organic solvent (D) dissolving the VdFpolymer (A) are, for instance, amide solvents such asN,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) andN,N-dimethylacetamide (DMAc); ketone solvents such as cyclohexane,methyl isobutyl ketone (MIBK) and 2-hetanone (MAK); ester solvents suchas butyl acetate and ethyl lactate; ether solvents such as ethylcellosolve and methyl cellosolve; and carbonate solvents such aspropylene carbonate and diethylene carbonate (DEC), and from theviewpoint of especially excellent solubility of the VdF polymer, amidesolvents are preferable. These solvents may be used alone or may bemixed optionally. Especially a solvent mixture comprising an amidesolvent as a main solvent and an ester, ketone, ether or carbonatesolvent as an auxiliary solvent has good wettability to a substrate andtherefore is suitable for forming a thin uniform film having less pinholes. Particularly for enhancing solubility of the VdF polymer (A), itis preferable to adjust a dielectric constant of a solvent to be notless than 22, and for improving coatability, it is preferable to adjusta surface tension of a solvent to be not more than 35 dyn/cm.

In addition to the solvent (D), to the coating composition may be addeda defoaming agent, a dispersant, a wetting agent, a leveling agent and aflowing agent as components not remaining in the film (disappearing atthe time of forming the film) or as components which do not givesubstantial influence on the effects (high dielectric constant,flexibility, formation of thin film) aimed at by the film of the presentinvention even if they are present in the film.

The coating composition is prepared by preparing an organic solvent (D)solution of the VdF polymer (A), optionally adding other componentsthereto, and then forcedly stirring and dispersing the mixture.Specifically there are the following methods for the preparation.

(1) A method of previously mixing, stirring and dispersing the component(B) and the component (C) in the solvent (D), and then sufficientlystirring and dispersing the obtained dispersed mixture and the VdFpolymer (A):

In this method, in the case where the affinity improving agent (C) isthe silane coupling agent (C1) or the epoxy group-containing compound(C3) which is a chemically reactive affinity improving agent, thecomponents (C) and (B) may be subjected to forced stirring anddispersing after the reaction thereof, or may be added to the solvent(D) and then subjected to the reaction and forced stirring anddispersing simultaneously, or the both may be carried out in combination(there is a case where this is referred to as surface treatment of thecomponent (B)). When the affinity improving agent is the surfactant(C2), since a reaction does not occur, it is easy to add the components(B) and (C) in the solvent (D) and then carry out the reaction andforced stirring and dispersing simultaneously.

For enhancing stability of a dispersed mixture of the components (B) and(C), it is desirable that a small amount of a solution of the VdFpolymer (A) is present when forcedly stirring and dispersing thecomponents (B) and (C).

(2) A method of adding the components (B) and (C) in a solvent (D)solution of the component (A) batchwise or in order and carrying outforced stirring and dispersing:

When adding in order, the order of adding is not limited particularly,and forced stirring and dispersing treatment may be carried out everytime when one component is added.

In any of the above-mentioned methods (1) and (2), it is desirable topreviously remove adsorbed water on a surface of the component (B) byheat treatment or the like since homogeneous dispersibility is furtherimproved. By subjecting the component (B) to pre-heat treatment orsurface treatment, homogeneous dispersing becomes easy even in the caseof the component (B) having a large average particle size. It isdesirable to undergo the both of pre-heat treatment and surfacetreatment.

A specified amount of each component may be added batchwise ordividedly. Further when adding dividedly, the adding order and thedivided addition may be combined freely, for example, in such a mannerthat a part of the component (A) is previously added when mixing thecomponents (B) and (C), and the remaining component (A) is added afterthe mixing, and further the component (C) is added and mixedadditionally.

Here an important point is to sufficiently carry out forced stirring anddispersing. If this dispersing treatment is insufficient, there is acase where solid contents such as the component (B) are easilyprecipitated, thereby making coating difficult, and in some cases, atforming a coating film by drying, phase separation occurs inside thefilm, and a uniform film being excellent in mechanical characteristicsand having stable dielectric characteristics cannot be formed. Thisforced stirring and dispersing treatment may be carried out for theprepared composition just before the coating.

The forced stirring and dispersing is to be carried out to such anextent that the composition after the stirring and dispersing does notcause phase separation (a change of turbidity of the solution is small(10% or less)) even in the case of allowing the composition to stand atroom temperature (25° C.) for seven days. A degree of the stirring anddispersing can be set by preliminary experiments.

Preferable examples of forced stirring and dispersing equipment are ballmill, sand mill, attrition mill, Visco Mill, roll mill, banbury mixer,stone mill, vibrator mill, dispersing mill, disc impeller, jet mill andDYNO-MILL. Among these, jet mill, roll mill and DYNO-MILL are preferablefrom the viewpoint that mixing of impurities hardly occurs andcontinuous production can be carried out.

Nonlimiting examples of the stirring and dispersing conditions are asfollows.

Equipment: Sand millStirring conditions:

-   -   Stirring speed: 100 to 10,000 rpm    -   Stirring time: 5 to 120 minutes    -   Others: Glass beads are used.

A film is formed using the obtained homogeneous coating composition. Itis preferable to carry out film formation by coating the composition ona substrate and then drying and if necessary, peeling the film from thesubstrate, from the viewpoint of easy working, a simple structure ofequipment and easy control of a film thickness. Also film formation maybe conducted by other film forming methods such as a method ofLangmuir-Blodgett's technique and an impregnation method.

For the coating, a knife coating method, a cast coating method, a rollcoating method, a gravure coating method, a blade coating method, a rodcoating method, an air doctor coating method, a curtain coating method,a Faknelane coating method, a kiss coating method, a screen coatingmethod, a spin coating method, a spray coating method, an extrusioncoating method, and an electrodeposition coating method can be employed.Among these, a roll coating method, a gravure coating method and a castcoating method are preferable from the viewpoint that operation is easy,non-uniformity of a film thickness is small and productivity issatisfactory.

Drying can be conducted using Yankee cylinder, counter flow, hot airblasting, air flow cylinder, air through, infrared ray, microwave, andinduction heating. For example, in the case of a hot air blastingmethod, the drying conditions of 130° to 200° C. for a period of time ofone minute or less are suitably adopted.

The highly dielectric film of the present invention may be left on asubstrate as a so-called coating film. When the film is used as a filmfor a film condenser, it is separated from a substrate and used in theform of a single film. Therefore preferable materials for a substrateare those from which a VdF polymer is easily peeled, for example,metallic sheets of stainless steel and copper; glass sheet; polymerfilms subjected to ITO and ZnO deposition; and polymer films having goodreleasing property. Examples of suitable polymer films are engineeringplastics such as polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyamide (PA), polyimide (PI),polyamide imide (PAI), polybenzimidazole (PBI), polyphenylene sulfide(PPS), polyphenylene oxide (PPO) and polysulfone (PSF).

When the film is left on a substrate as a coating film, the compositionof the present invention can be coated on a polymer film and dried tomake a laminated film. Preferable as a substrate for the laminated filmare polymer films which have good adhesion to the VdF polymer (A) andhave a thickness of about 1.5 to 3 μm. Examples of suitable polymers areengineering plastics such as PET, PEN, PC, PA, PI, PAI, PBI, PPS, PPOand polysulfone (PSF).

A single film is used as it is, and may be stretched by usual method. Inthat case, a stretching ratio is desirably about 2 to 6 times.

In any of single films and laminated films, they may be subjected tosurface treatment with other kind of polymer or plasma treatment orcorona discharge treatment in order to make deposition of aluminum foran electrode easy. In addition, in order to inhibit roughening of a filmsurface, other kind of polymer may be coated on a film surface, and inorder to improve film strength, a film may be subjected to crosslinkingtreatment with ultraviolet ray, electron beam or radiation. Further, afilm may be subjected to pressing, for example, pressing with rolls. Inthat case, surface smoothness of a film is improved.

A thickness of the so-obtained highly dielectric film of the presentinvention can be not more than 9 μm, preferably not more than 6 μm,further preferably not more than 5 μm. A lower limit of the filmthickness varies depending on kind of a polymer and a particle size andan amount of the component (B), and is about 3 μm from the viewpoint ofmaintaining mechanical strength of a film.

In the highly dielectric film of the present invention, in spite of thecontent of specific titanium oxide particles (B) being relatively high(60% by mass or more), a film thickness can be made thin, and thereforeelectrostatic capacity can be made high. For example, when bariumtitanate particles having a dielectric constant of 2,000 are used as thecomponent (B) and a content thereof is 100% by mass, a dielectricconstant of the film can be 30 or more. In this case, assuming an areaof a circular electrode is 9.5 mm², an electrostatic capacity of a filmhaving a thickness of 9 μm is 2.8 nF or more, and an electrostaticcapacity of a film having a thickness of 6 μm is 4.2 nF or more.

Also according to the film of the present invention, since the specifictitanium oxide particles (B) are bonded firmly to the VdF polymer (A) byan action of a coupling agent or a surfactant, a dense structure havinga small void content (for example, not more than 5% by volume, furthernot more than 1% by volume) is obtained and a withstand voltage can bemade high.

In spite of a dense structure, the film of the present invention isexcellent in flexibility (winding property). For example, in the case ofa 5 μm thick film, neither cracking nor breaking occurs at 180 degreebending test. Therefore when the film is used for a film condenser,processability (winding property and followability) are significantlyimproved.

The film of the present invention is excellent in surface smoothness,and for example, surface roughness of its center can be not more than ±1μm, further not more than ±0.6 μm. Uniformity of electricalcharacteristics is improved due to excellent surface smoothness.

When the highly dielectric film of the present invention is used, forexample, as a film for a film condenser, an electrode can be formed onits surface by a deposition method or the like. With respect to amaterial of an electrode, and a method and conditions for forming anelectrode, those generally known can be employed.

The highly dielectric film of the present invention is useful especiallyas a film for a film condenser, and also useful as a film forpiezoelectric element, a film for a pyroelectric device, a dielectricfilm for transfer printing carrier and a film for strong dielectricelement.

EXAMPLES

The present invention is then explained by means of Examples, but is notlimited to them.

Characteristic values used herein are those measured by the followingmethods.

(Viscosity)

For measuring a viscosity, a cone plate viscometer VISCONE CV Seriesavailable from Misec Corporation is used. Measuring conditions are roomtemperature and the number of rotations of 94 rpm, and No. 2 cone (10p)is used.

(Dispersion Stability)

A dispersion is poured in a 50 ml glass sample bottle and allowed tostand at room temperature. One week after, dispersibility is observedwith naked eyes. When homogeneity is kept, it is evaluated as ◯, andwhen precipitation occurs, it is evaluated as X.

(Dielectric Constant)

Using a film of a mixture of a polymer and inorganic particles formed ona metallic substrate or a film of a mixture of a polymer and inorganicparticles subjected to aluminum deposition on one surface thereof, asample is produced by aluminum deposition in vacuo on a 95 mm² area of afilm surface opposite to the substrate (or the aluminum-depositedsurface). An electrostatic capacity and a dielectric loss of this sampleare measured at room temperature (25° C.) at a frequency of 100 Hz, 1kHz, 10 kHz and 100 kHz using an impedance analyzer (HP4194A availablefrom Hewlett Packard).

(Film Thickness)

A thickness of a film on a substrate is measured at room temperatureusing a film thickness meter (CMI223 available from Oxford Instruments)adjusting zero point depending on a substrate and calibrated bytwo-point reference thicknesses.

(Flexibility)

After bending a film having a length of 20 mm, a width of 5 mm and athickness of 5 μm by 180 degrees, cracking and deformation at a bentportion are observed with naked eyes. When there is neither cracking nordeformation at the bent portion, it is evaluated as ◯.

(Content of Void)

A theoretical density P of a film comprising (1−w) part by weight of apolymer having a density PA and w part by weight of inorganic particleshaving a density PB is shown by the following equation.

P=(1−w)PA+wPB

A void ratio α (%) of a film is calculated by the following equationfrom a real density PC of the film obtained by a density grading method.

α(%)={1−(P/PC)×100}

(Surface Center Roughness)

For measuring surface center roughness, SURFTEST SV-600 available fromMitsutoyo Corporation is used, and an arithmetic mean roughness (Ra) isdetermined according to JIS B 0601-1994.

(Observation with Scanning Electron Microscope (SEM))

Microscope: S-4000 available from Hitachi, Ltd.

Example 1

Into a 3-liter separable flask were poured 900 parts by mass ofN-methylpyrrolidone (NMP) (available from Tokyo Chemical Industry Co.,Ltd.) and 100 parts by mass of polyvinylidene fluoride (PVdF) polymer(VP832 available from DAIKIN INDUSTRIES, LTD., dielectric constant: 9.8(1 kHz, 25° C.)), and 4-hour stirring was carried out at 80° C. undernitrogen gas atmosphere with a mechanical stirrer to obtain a polymersolution having a concentration of 10% by mass. This polymer solutionwas a light-yellow homogeneous solution.

To this NMP solution of PVdF were added 100 parts by mass of bariumtitanate (BT-01 available from Sakai Chemical Industry Co., Ltd.) havingan average particle size of 0.1 μm and further 10 parts by mass ofPLANEACT KR-55 available from AJINOMOTO CO., INC. as a titanium couplingagent.

To this mixture was added the same mass of glass beads (GB503M availablefrom Potters-Ballotini Co., Ltd.) as that of the mixture, and theobtained mixture was put in a water-cooled three drum type sand grinder(A•VIEX available from AIMEX), followed by 60-minute dispersingtreatment at room temperature at 1,000 rpm. After the dispersingtreatment, the mixture was passed through a stainless steel mesh toremove glass beads and obtain the composition of the present invention.

A viscosity and dispersion stability of this composition were evaluated.The results are shown in Table 1.

Then the obtained composition was coated on a stainless steel substratewith a bar coater, and dried with hot air at 180° C. for one minute toform an about 5.1 μm thick dielectric film.

A dielectric constant at each frequency, flexibility, surface centerroughness and void content of the obtained film were evaluated. Theresults are shown in Table 1.

Examples 2 to 10

Compositions of the present invention were prepared in the same manneras in Example 1 except that amounts of PVdF, barium titanate and atitanium coupling agent were changed as shown in Table 1, and aviscosity and dispersion stability thereof were evaluated. Furtherdielectric films were formed in the same manner as in Example 1, and adielectric constant at each frequency, flexibility, surface centerroughness and void content of the obtained films were evaluated. Theresults are shown in Table 1.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 Composition (part by mass) Solvent(NMP) 900 900 850 800 850 900 900 900 900 900 PVdF 100 100 150 200 150100 100 100 100 100 Barium titanate 100 150 225 300 225 150 150 150 150150 Coupling agent 10 15 22.5 30 11.3 1.5 15 15 7.5 1.5 Characteristicsof composition Dispersion stability ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Viscosity (Pa ·s) 0.58 0.58 1.45 1.58 0.59 0.59 0.59 0.59 0.59 0.59 Characteristics offilm Film thickness (μm) 5.1 5.2 4.8 5.2 4.9 5.0 3.2 8.4 6.5 7.2Dielectric 100 Hz 37 65 64 63 64 64 64 64 63 61 constant  1 kHz 35 60 6362 62 62 63 63 61 59  10 kHz 34 58 59 59 60 60 59 59 58 57 100 kHz 31 5556 57 58 58 56 56 55 53 Flexibility ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ Surface centerroughness (μm) 0.4 0.5 1.5 1.8 0.6 0.5 0.4 0.5 0.4 0.4 Content of void(%) <1 <1 <1 <1 <1 <1 <1 <1 <1 <1

Examples 11 to 24

Compositions of the present invention were prepared in the same manneras in Example 1 except that various surfactants were added in an amountof 10% by mass based on barium titanate instead of the titanium couplingagent and amounts of PVdF and barium titanate were changed as shown inTable 2, and dispersion stability thereof was evaluated. Furtherdielectric films were formed in the same manner as in Example 1, and adielectric constant at each frequency and flexibility of the obtainedfilms were evaluated. The results are shown in Table 2.

Added surfactants S1 to S13 are as follows.

S1: Nonionic surfactant (poly-oxyethylene-distyrene-phenyl-ether)(EMULGEN A60 available from KAO CORPORATION)S2: Anionic surfactant (special polycarboxylic acid polymer surfactant)(HOMOGENOL L18 available from KAO CORPORATION)S3: Cationic surfactant (imidazoline surfactant) (HOMOGENOL L95available from KAO CORPORATION)S4: Nonionic surfactant (sorbitan monooleate) (REODOL sp10 availablefrom KAO CORPORATION)S5: Nonionic surfactant (alkylglukoxide) (MIDOL 10 available from KAOCORPORATION)S6: Cationic surfactant (amine type polymer surfactant) (DisperByk 180available from BYK-Chemie GmbH)S7: Anionic surfactant (carboxylic acid polymer surfactant) (DisperByk182 available from BYK-Chemie GmbH)S8: Anionic surfactant (poly-ester-acid amine salt) (ED117 availablefrom KUSUMOTO CHEMICALS, LTD.)S9: Anionic surfactant (poly-carboxylic acid-amide amine salt with highMw) (ED211 available from KUSUMOTO CHEMICALS, LTD.)S10: Anionic surfactant (poly-ether-ester-amine salt with high Mw)(ED214 available from KUSUMOTO CHEMICALS, LTD.)S11: Cationic surfactant (chlorinated alkyltrimethyl ammonium) (ArcadeT50 available from LION CORPORATION)S12: Cationic surfactant (chlorinated alkylbis(2-hydroxyethyl)methylammonium salt) (ESOCARD C12 available from LION CORPORATION)S13: Anionic surfactant (polyoxyethylene alkylamine) (EnomineC12available from LION CORPORATION)

TABLE 2 Example 11 12 13 14 15 16 17 Composition (part by mass) Solvent(NMP) 900  900  900  900  850  900  900  PVdF 100  100  100  100  150 100  100  Barium titanate 100  100  100  100  150  100  100  SurfactantS1 S2 S3 S4 S5 S6 S7 (amount) (10) (10) (10) (10) (15) (10) (10)Characteristics of composition Dispersion stability ◯ ◯ ◯ ◯ ◯ ◯ ◯Characteristics of film Film thickness (μm)   5.2   4.8   5.5   5.2  4.9   5.5   5.4 Dielectric constant 100 Hz 33 36 41 29 28 29 29  1 kHz25 34 26 29 23 26 28  10 kHz 22 33 19 26 21 22 27 100 kHz 21 32 15 25 2020 24 Flexibility ◯ ◯ ◯ ◯ ◯ ◯ ◯ Example 18 19 20 21 22 23 24 Composition(part by mass) Solvent (NMP) 800  800  800  800  800  800  800  PVdF200  200  200  200  200  200  200  Barium titanate 300  300  300  300 300  300  300  Surfactant S3 S8 S9 S10 S11 S12 S13 (amount) (30) (30)(30) (30) (30) (30) (30) Characteristics of composition Dispersionstability ◯ ◯ ◯ ◯ ◯ ◯ ◯ Characteristics of film Film thickness (μm)  4.5   5.5   4.7   5.1   5.1   4.1   4.9 Dielectric constant 100 Hz 6631 40 38 2673  3424  22  1 kHz 41 27 37 34 281  1119  20  10 kHz 31 2736 33 83 327  19 100 kHz 26 26 34 32 42 88 18 Flexibility ◯ ◯ ◯ ◯ ◯ ◯ ◯

Comparative Examples 1 to 3

Compositions for comparison were prepared in the same manner as inExample 1 except that a titanium coupling agent was not added, PVdF andbarium titanate were added in amounts as shown in Table 3, anddispersion treatment was not carried out in Comparative Examples 1 and2, and a viscosity and dispersion stability thereof were evaluated.Further dielectric films were formed in the same manner as in Example 1,and a dielectric constant at each frequency, flexibility, surface centerroughness and content of void of the obtained films were evaluated. Theresults are shown in Table 3.

TABLE 3 Comparative Example 1 2 3 Composition (part by mass) Solvent(NMP) 900 900 850 PVdF 100 100 150 Barium titanate 100 150 225Dispersion treatment none none conducted Characteristics of compositionDispersion stability X X X Viscosity (Pa · s) 0.56 0.58 1.45Characteristics of film Film thickness (μm) 5.5 5.1 4.8 Dielectricconstant 100 Hz 12 21 22  1 kHz 12 20 21  10 kHz 11 19 19 100 kHz 10 1716 Flexibility ◯ ◯ ◯ Surface center roughness (μm) 1.5 2.1 1.8 Contentof void (%) 4.5 5.0 4.5

Comparative Example 4

A composition for comparison was prepared in the same manner as inExample 1 according to the same formulations as in Example 1 except thataromatic polyamide imide (HI680 available from Hitachi Chemical Co.,Ltd.) was used as a polymer instead of PVdF, and dispersion stabilitythereof was evaluated. Further a dielectric film was formed in the samemanner as in Example 1, and a dielectric constant at each frequency,flexibility and void content of the obtained film were evaluated. Theresults are shown in Table 4.

A film having a thickness of not more than 10 μm could not be formedbecause the obtained film was low in flexibility and fragile.

Comparative Example 5

A composition for comparison was prepared in the same manner as inExample 1 according to the same formulations as in Example 12 exceptthat aromatic polyamide imide (HI680 available from Hitachi ChemicalCo., Ltd.) was used as a polymer instead of PVdF and 150 pats by mass ofbarium titanate was used, and dispersion stability thereof wasevaluated. Further a dielectric film was formed in the same manner as inExample 1, and a dielectric constant at each frequency, flexibility andvoid content of the obtained film were evaluated. The results are shownin Table 4.

A film having a thickness of not more than 10 μm could not be formedbecause the obtained film was low in flexibility and fragile.

TABLE 4 Comparative Example 4 5 Composition (part by mass) Solvent (NMP)900 900 Aromatic polyamide imide 100 100 Barium titanate 100 150Additive Titanium Surfactant S2 coupling agent (15) (10) Characteristicsof composition Dispersion stability X X Characteristics of film Filmthickness (μm) 12.2 12.5 Dielectric constant 100 Hz 6 7  1 kHz 6 7  10kHz 5 6 100 kHz 4 5 Flexibility X X Content of void (%) 2.0 2.0

SEM photographs of the films obtained in Examples 2, 3 and 18 andComparative Example 3, respectively are shown in FIGS. 1 to 8.

The relation of each example to Fig. number is Example 2 (FIG. 1: 1,000magnifications, FIG. 2: 10,000 magnifications), Example 3 (FIG. 3: 1,000magnifications, FIG. 4: 10,000 magnifications), Example 18 (FIG. 5:1,000 magnifications, FIG. 6: 10,000 magnifications), and ComparativeExample 3 (FIG. 7: 1,000 magnifications, FIG. 8: 10,000 magnifications).

It can be seen from these photographs that the surface of the film ofthe present invention is dense, homogeneous and smooth.

Example 25 Heat Treatment and Preliminary Treatment with AffinityImproving Agent of Barium Titanate Particles

Barium titanate particles (BT-01 available from Sakai Chemical IndustryCo., Ltd.) were subjected to the following heat treatment and surfacetreatment.

(Heat Treatment)

Barium titanate particles were subjected to drying treatment at 250° C.for two hours with hot air to remove adsorbed water.

(Surface Treatment)

The heat-treated barium titanate particles and a titanium coupling agent(PLANEACT KR-55 available from AJINOMOTO CO., INC.) in an amount of 5%by mass based on barium titanate particles were forcedly stirred inhexane for 30 minutes with a sand grinder, and then a supernatant wassubjected to decantation and then drying at 150° C. for two hours toobtain barium titanate particles surface-treated with the titaniumcoupling agent.

In 3-liter separable flask, a solution of a mixture ofN,N-dimethylacetamide (DMAc) (available from Kishida Chemical Co., Ltd.)and methyl isobutyl ketone (MIBK available from Kishida Chemical Co.,Ltd.) (mass ratio of 24.3/19.5) was added to a solution obtained bydissolving a polyvinylidene fluoride (PVdF) polymer (VP832 availablefrom DAIKIN INDUSTRIES, LTD., dielectric constant of 9.8 (1 kHz, 25°C.)) in DMAc to adjust the concentration of PVdF to 2.5% by mass.

To 40 parts by mass of this DMAc solution of PVdF were added 50 parts bymass of the surface-treated barium titanate particles and 2.5 parts bymass of a titanium coupling agent (PLANEACT KR-55).

To the obtained mixture were added glass beads (GB503M available fromPotters-Ballotini Co., Ltd.) in an amount of 1.2 times that of themixture. The resultant mixture was poured into a water-cooled three drumtype sand grinder (A•VIEX available from AIMEX), and 60-minute stirringand dispersing treatment was carried out at room temperature at 1,500rpm. The mixture after the dispersing treatment was passed through astainless steel mesh (available from MANABE KOGYO CO., LTD., 80 mesh) toremove the glass beads and prepare a dispersion of barium titanate.

Then the obtained dispersion of barium titanate (70 parts by mass), DMAcsolution of PVdF having a concentration of 20% by mass (100 parts bymass), DMAc (19 parts by mass) and MIBK (66 parts by mass) were mixed,and thereto were added glass beads in an amount of 1.2 times that of themixture. The resultant mixture was poured into a water-cooled three drumtype sand grinder, followed by forced stirring at 1,500 rpm for twohours to prepare the coating composition of the present invention. Thiscomposition was in a homogeneously dispersed state (evaluation: ◯).

The obtained composition was then coated on an aluminum substrate with abar coater, and dried at 180° C. for one minute with hot air to form anabout 4.7 μm thick dielectric film (Film 1).

A dielectric constant at each frequency and a dielectric loss tangent ofthe obtained film were determined. The results are shown in Table 5.

Also dispersibility (coating composition) and a dielectric constant ateach frequency and a dielectric loss tangent (film) were determined withrespect to a coating composition prepared by using barium titanateparticles (BT-01) surface-treated with a titanium coupling agent but notsubjected to heat treatment and a film obtained therefrom (Film 2); acoating composition prepared by using barium titanate particles (BT-01)heat treated but not subjected to surface-treatment with a titaniumcoupling agent and a film obtained therefrom (Film 3); and a coatingcomposition prepared by using barium titanate particles subjected toneither heat treatment nor surface-treatment with a titanium couplingagent and a film obtained therefrom (Film 4). The results are shown inTable 5.

TABLE 5 Film Number 1 2 3 4 Composition (part by mass) PVdF (solidcontent) 100 100 100 100 Barium titanate 180 180 180 180 Heat treatmentconducted none conducted none Surface treatment conducted conducted nonenone Titanium coupling agent 18 18 9 9 (an amount used for (9) (9) (0)(0) surface treatment) Solvent DMAc 540 540 540 540 MIBK 360 360 360 360Characteristics of composition Dispersibility ◯ ◯ ◯ ◯ Characteristics offilm Film thickness (μm) 4.7 5.1 5.1 4.8 Dielectric constant 100 Hz 186132 58 67  1 kHz 70 78 51 57  10 kHz 48 62 47 52 100 kHz 40 55 43 47Dielectric loss tangent (%) 100 Hz 194 93 14 16  1 kHz 83 36 8 10  10kHz 27 14 6 7 100 kHz 11 10 18 19

Example 26

A coating composition was prepared by conducting preliminary heattreatment and surface treatment in the same manner as in the productionof Film 1 of Example 25 except that barium titanate particles having anaverage particle size of 30 nm (BTO-30RP available from TODA KOGYOCORP.) were used as barium titanate particles. Dispersibility thereof isshown in Table 6.

Further a film was produced by using this composition, and a dielectricconstant at each frequency and a dielectric loss tangent weredetermined. The results are shown in Table 6.

TABLE 6 Example 26 Composition (part by mass) PVdF (solid content) 100Barium titanate 180 Heat treatment conducted Surface treatment conductedTitanium coupling agent 18 (an amount used for (9) surface treatment)Solvent DMAc 540 MIBK 360 Characteristics of composition Dispersibility◯ Characteristics of film Film thickness (μm) 3.4 Dielectric constant100 Hz 111  1 kHz 64  10 kHz 52 100 kHz 46 Dielectric loss tangent (%)100 Hz 113  1 kHz 38  10 kHz 14 100 kHz 11

Example 27

Into a separable flask were poured 3,200 parts by mass ofN,N-dimethylacetamide (DMAc) (available from Kishida Chemical Co., Ltd.)and 800 parts by mass of a polyvinylidene fluoride (PVdF) polymer (KYNAR761 available from ARKEMA, dielectric constant of 9.6 (100 kHz, 25°C.)), and 3-hour stirring was carried out at 80° C. under nitrogen gasatmosphere with a mechanical stirrer to obtain a solution of PVdF havinga concentration of 20% by mass. This polymer solution was a transparenthomogeneous solution.

To 4,000 parts by mass of this DMAc solution of PVdF were added 1,120parts by mass of DMAc and 2,280 parts by mass of methyl isobutyl ketone(MIBK) so that the polymer concentration became 10% by mass.

To 2,000 parts by mass of the obtained PVdF/DMAc/MIBK solution wereadded 350 parts by mass of barium titanate having an average particlesize of 0.1 μm (BT-01 available from Sakai Chemical Industry Co., Ltd.)and 17.5 parts by mass of PLANEACT KR-55 available from AJINOMOTO CO.,INC. as a titanium coupling agent, followed by about 10-minute stirringwith a homogenizer.

This mixture was subjected to forced stirring and dispersing treatmentby a pass method at a peripheral speed of 8 m/sec by using DYNO-MILL(model MULTI-LAB available from WA Bachofen AG) by filling glass beads(average particle size of 0.5 to 0.7 mm) at a filling ratio of 80%. Thusthe respective coating compositions of the present invention wereobtained in the number of passes of 1 to 5.

The pass method of DYNO-MILL is a method of circulating slurry between atank and a beads mill, and passing the beads mill once is assumed to beone pass.

Dispersion stability of the obtained coating compositions wasdetermined. The results are shown in Table 7.

Then the obtained coating compositions were coated on an aluminumsubstrate with a bar coater, and dried with hot air at 180° C. for oneminute to form dielectric films.

A thickness, a dielectric constant at each frequency and a dielectricloss tangent of the obtained films were determined. The results areshown in Table 7.

TABLE 7 Number of passes 1 2 3 4 5 Composition (part by mass) PVdF(solid content) 100 100 100 100 100 Barium titanate 180 180 180 180 180Titanium coupling agent 9 9 9 9 9 Solvent DMAc 540 540 540 540 540 MIBK360 360 360 360 360 Characteristics of composition Dispersibility ◯ ◯ ◯◯ ◯ Characteristics of film Film thickness (μm) 4.1 3.5 3.9 3.4 3.9Dielectric constant 100 Hz 64 62 64 54 56  1 kHz 56 51 53 45 45  10 kHz45 49 48 40 40 100 kHz 45 43 45 38 37 Dielectric loss tangent (%) 100 Hz20 22 20 21 26  1 kHz 10 11 10 11 12  10 kHz 9 6 6 6 7 100 kHz 9 7 9 7 8

Example 28

Barium titanate particles (BT-01 available from Sakai Chemical IndustryCo., Ltd.) were subjected to the following heat treatment and surfacetreatment.

(Heat Treatment)

Barium titanate particles were subjected to drying at 250° C. for twohours with hot air to remove adsorbed water.

(Surface Treatment)

500 parts by mass of the heat-treated barium titanate particles and 25parts by mass of glycidyl methacrylate (GMA) were forcedly stirred in500 parts by mass of hexane for one hour with a mechanical stirrer, andthen dried at 150° C. for evaporating hexane to obtain barium titanateparticles surface-treated with GMA.

Into a 3-liter separable flask were poured 800 parts by mass ofN,N-dimethylacetamide (DMAc) (available from Kishida Chemical Co., Ltd.)and 200 parts by mass of a polyvinylidene fluoride (PVdF) polymer (KYNAR761 available from ARKEMA), and 4-hour stirring was carried out at 80°C. under nitrogen gas atmosphere with a mechanical stirrer to obtain aDMAc solution of PVdF having a concentration of 20% by mass.

500 parts by mass of the barium titanate particles surface-treated withGMA, 242.5 parts by mass of DMAc, 195 parts by mass of methyl isobutylketone (MIBK) and 62.5 parts by mass of the obtained DMAc solution ofPVdF having a concentration of 20% by mass were mixed, and furtherthereto was added 25 parts by mass of GMA, followed by one-hour stirringand mixing with a rotor.

To the obtained mixture were added glass beads (GB503M available fromPotters-Ballotini Co., Ltd.) in an amount of 1.2 times that of themixture, and the resultant mixture was poured into a water-cooled threedrum type sand grinder (A•VIEX available from AIMEX), followed by60-minute stirring and dispersing treatment at room temperature at 1,500rpm. The mixture after the dispersing treatment was passed through astainless steel mesh (available from MANABE KOGYO CO., LTD., 80 mesh) toremove the glass beads and prepare a dispersion of barium titanate.

Then the obtained dispersion of barium titanate (300.04 parts by mass),the DMAc solution of PVdF having a concentration of 20% by mass (400parts by mass), DMAc (46.2 parts by mass) and MIBK (244.1 parts by mass)were mixed, followed by forced stirring for one hour with a rotor(BIG-ROTORS BR-2 available from AS-ONE) to prepare the coatingcomposition of the present invention.

The obtained composition was then coated on a stainless steel substratewith a bar coater, and dried at 180° C. for two minutes with hot air toform an about 5 μm thick dielectric film (Film 5).

A dielectric constant and a dielectric loss tangent at 10 kHz of theobtained film were determined. The results are shown in Table 8.

Also a dielectric constant and a dielectric loss tangent at 10 kHz weredetermined with respect to a coating composition prepared by usingbarium titanate particles (BT-01) surface-treated with GMA but notsubjected to heat treatment without adding GMA in the preparation stepof the composition and a film obtained therefrom (Film 6); and a coatingcomposition prepared by using barium titanate particles (BT-01)subjected to heat treatment and surface-treatment with GMA withoutadding GMA in the preparation step of the composition and a filmobtained therefrom (Film 7). The results are shown in Table 8.

TABLE 8 Film Number 5 6 7 Composition (part by mass) PVdF (solidcontent) 100 100 100 Barium titanate 175 175 175 Heat treatmentconducted none conducted Surface treatment conducted conducted conductedGMA 17.5 8.8 8.8 (an amount used for (8.8) (8.8) (8.8) surfacetreatment) Solvent DMAc 541 541 541 MIBK 360 360 360 Characteristics ofcomposition Dispersibility ◯ ◯ ◯ Characteristics of film Film thickness(μm) 5.0 4.8 5.2 Dielectric constant 10 kHz 55 47 47 Dielectric losstangent (%) 10 kHz 11 10 12

Example 29

Solubility of PVdF in the solvents (D) shown in Table 9 were evaluatedby the following method. The results are shown in Table 9.

(Solubility)

1 g each of PVdF was added to 5 g of the respective solvents, and afterstirring at 25° C. for 10 minutes with a mechanical stirrer, thesolutions were allowed to stand for one hour, and then a state of thesolutions was observed with naked eyes.

The evaluation is made by the following criteria.

◯: A solution is colorless and transparent and no gelling occurs.X: A solution is turned turbid and gelling occurs.

Next, coatability of the obtained solution of PVdF was evaluated by thefollowing method. The results are shown in Table 9.

(Coatability)

A solution of PVdF is coated on a polyester film with a bar coater, anddried with hot air at 180° C. for one minute to make a film. Theobtained film is observed with naked eyes to check to see whether or nota pin hole is present on the film. When a pin hole is found, it isindicated by X, and when no pin hole is found, it is indicated by ◯.

The solvents used in this Example are as follows. A dielectric constantand a surface tension of each of the solvents are values shown in theSolvent Handbook (Yuasa et al., Kodansha Ltd. (1976)). In the case of asolvent mixture, a dielectric constant and a surface tension thereof arevalues calculated from an arithmetic mean value in a mass ratio of eachsolvent.

NMP: N-methylpyrrolidone (available from Kishida Chemical Co., Ltd.),dielectric constant (25° C.): 32, surface tension (25° C.): 41 dyn/cmDMF: N,N-dimethylformamide (available from Kishida Chemical Co., Ltd.),dielectric constant (25° C.): 36.71, surface tension (25° C.): 35.2dyn/cmDMAc: N,N-dimethylacetamide (available from Kishida Chemical Co., Ltd.),dielectric constant (25° C.): 37.78, surface tension (30° C.): 32.43dyn/cmMIBK: Methyl isobutyl ketone (available from Kishida Chemical Co.,Ltd.), dielectric constant (20° C.): 13.11, surface tension (25° C.):25.4 dyn/cmMAK: 2-Heptanone (available from Kishida Chemical Co., Ltd.), dielectricconstant (22° C.): 9.77, surface tension (25° C.): 34.5 dyn/cmDEC: Diethylene carbonate (available from Tokyo Chemical Industry Co.,Ltd.), dielectric constant (20° C.): 2.820, surface tension (30° C.):25.47 dyn/cm

TABLE 9 Mixing ratio Surface (mass Dielectric tension Solvent ratio)constant (dyn/cm) Solubility Coatability NMP — 32 41 ◯ ◯ DMF — 36.7135.2 ◯ ◯ DMAc — 37.78 32.43 ◯ ◯ DMF/MIBK 60/40 27.3 31.3 ◯ ◯ DMF/MAK60/40 25.9 34.9 ◯ ◯ DMF/DEC 60/40 23.2 31.3 ◯ ◯ DMAc/ 60/40 27.9 29.6 ◯◯ MIBK DMAc/MAK 60/40 26.6 33.2 ◯ ◯ DMAc/DEC 60/40 23.8 29.6 ◯ ◯

Example 30

Into a 5-liter separable flask were poured 800 parts by mass ofN,N-dimethylacetamide (DMAC) (available from Kishida Chemical Co., Ltd.)and 200 parts by mass of a polyvinylidene fluoride (PVdF) polymer (KYNAR761 available from ARKEMA), and 3-hour stirring was carried out at 80°C. under nitrogen gas atmosphere with a mechanical stirrer to obtain aDMAc solution of PVdF having a concentration of 20% by mass. Thissolution was a transparent homogeneous solution.

To 62.5 parts by mass of this DMAc solution of PVdF having aconcentration of 20% by mass were added 242.5 parts by mass of DMAc and195 parts by mass of MIBK to adjust the PVdF concentration to 2.5% bymass. Then thereto were added 500 parts by mass of barium titanate(BT-01 available from Sakai Chemical Industry Co., Ltd.) and 25 parts bymass of a titanium coupling agent (PLANEACT KR-55 available fromAJINOMOTO CO., INC.).

To the obtained mixture were added glass beads (GB503M available fromPotters-Ballotini Co., Ltd.) in an amount of 1.2 times that of themixture, and the resultant mixture was poured into a water-cooled threedrum type sand grinder (A•VIEX available from AIMEX), followed by60-minute stirring and dispersing treatment at room temperature at 1,500rpm. The mixture after the dispersing treatment was passed through astainless steel mesh (available from MANABE KOGYO CO., LTD., 80 mesh) toremove the glass beads and prepare a dispersion of barium titanate.

Then the obtained dispersion of barium titanate (1,500 parts by mass),the DMAc solution of PVdF having a concentration of 2.5% by mass (2,000parts by mass), DMAc (231 parts by mass) and MIBK (1,220 parts by mass)were mixed and forcedly stirred for two hours with a mechanical stirrer,followed by filtration with a stainless steel mesh (available fromMANABE KOGYO CO., LTD., 200 mesh) to prepare the coating composition ofthe present invention. This composition was in a homogeneously dispersedstate.

The obtained coating composition was coated on a polyester film (38 μmthick) by using a micro gravure coater (OS-300 available from YASUISEIKI CO., LTD.) at 1.2 rpm of a 45 mesh micro gravure roll at aperipheral speed of 5 m/min, and the coated film was passed 6 m in adrying oven of 150° C. and then passed 6 m in a drying oven of 180° C.Thus two 100 m long laminated films having a coating layer of 200 mmwide×5.2 μm thick (dielectric film layer) were prepared.

The coating layer was peeled from the laminated film and wound at aperipheral speed of 1.5 m/min to obtain a dielectric film of 200 mmwide×5.2 μm thick.

Example 31

A dispersion was prepared and a dielectric film was produced in the samemanner as in Example 27 except that 400 parts by mass of polyvinylidenefluoride (PVdF) (KYNAR 761 available from ARKEMA) and 400 parts by massof polyvinylidene fluoride/hexafluoropropylene copolymer (KYNAR 2801available from ARKEMA) were used as a polymer component.

A film thickness, a dielectric constant and a dielectric loss tangent ateach frequency of the obtained film were determined. As a result, thefilm thickness was 5.2 μm; the dielectric constants were 65, 58, 51 and48 at 100 Hz, 1 kHz, 10 kHz and 100 kHz, respectively; and thedielectric loss tangents (%) were 12, 8, 4 and 4 at 100 Hz, 1 kHz, 10kHz and 100 kHz, respectively.

Example 32

The film produced in Example 27 was subjected to press-treatment bypassing through two calendar rolls at a speed of 1 m/min at 60° C. and120° C. at a load of 1 ton and 4 tons. In order to evaluate surfacesmoothness of the press-treated film, a reflectance was measured by thefollowing method.

[Measuring Method of Reflectance]

A reflectance of a thin film is measured in an applied measuring mode byusing a spectrophotometer (U-4100) and a 5C plus reflection attachedequipment available from Hitachi High-Technologies Corporation.

A visible light reflectance (% R) measured at a scanning speed of 300nm/min at a wavelength of 1,000 to 300 nm is assumed to be areflectance.

As a result, while a reflectance of an untreated film was 0.31%,reflectances in the cases of press-treatment at 60° C. at a load of 1ton, press-treatment at 60° C. at a load of 4 tons, press-treatment at120° C. at a load of 1 ton and press-treatment at 120° C. at a load of 4tons were 0.41%, 0.56%, 1.05% and 1.91%, respectively. Thus surfacesmoothness was improved.

Example 33

The film produced in Example 31 was subjected to press-treatment bypassing through two calendar rolls at a speed of 1 m/min at 120° C. at aload of 1 ton and 4 tons. In order to evaluate surface smoothness of thepress-treated film, a reflectance was measured by the method of Example34.

As a result, while a reflectance of an untreated film was 0.31%, areflectance in the case of press-treatment at 120° C. at a load of 1 tonwas 4.32% and a reflectance in the case of press-treatment at 120° C. ata load of 4 tons was 4.38%. Thus surface smoothness was greatlyimproved.

Example 34

To 50 parts by mass of a methyl ethyl ketone (MEK) solution were added50 parts by mass of barium titanate having an average particle size of0.1 μm (BT01 available from Sakai Chemical Industry Co., Ltd.) and 2.5parts by mass of PLANEACT KR55 (available from AJINOMOTO CO., INC.) as atitanium coupling agent.

Into a three drum type sand grinder (A•VIEX available from AIMEX) werepoured this mixture and glass beads (GB503M available fromPotters-Ballotini Co., Ltd.) in the same mass amount, followed by60-minute dispersion treatment at room temperature at 1,000 rpm. Afterthe dispersing treatment, the mixture was passed through a stainlesssteel mesh to remove the glass beads.

This dispersion solution was added to a 20% by mass MEK solution of aVdF/TFE copolymer (84/16 in molar ratio) so that the amount of bariumtitanate became 100% by mass based on the VdF/TFE copolymer. Theobtained solution was coated on an aluminum substrate with a bar coater,and dried at 120° C. for two minutes with a hot air dryer to obtain a5.5 μm thick highly dielectric film of the present invention. Thenphysical properties of the film were measured.

As a result, a dielectric constant was 31, and a dielectric loss tangent(%) was 3.2.

INDUSTRIAL APPLICABILITY

The highly dielectric film of the present invention has high dielectricconstant, can be formed into a thin film, is excellent in windingproperty (flexibility), and yet can be easily produced by a simplemethod.

1. A highly dielectric film comprising: (A) a vinylidene fluoridepolymer, (B) barium titanate oxide particles and/or lead zirconiumtitanate oxide particles, and (C) an affinity improving agent comprisingat least one kind of a coupling agent, a surfactant or an epoxygroup-containing compound, wherein said barium titanate oxide particlesand/or lead zirconium titanate oxide particles (B) and said affinityimproving agent (C) are contained in amounts of 10 to 500 parts by massand 0.01 to 30 parts by mass, respectively based on 100 parts by mass ofthe vinylidene fluoride polymer (A).
 2. The highly dielectric film ofclaim 1, wherein the affinity improving agent (C) is a coupling agentand/or a surfactant.
 3. The highly dielectric film of claim 2, whereinthe coupling agent is a titanium coupling agent, a silane couplingagent, a zirconium coupling agent or a zircoaluminate coupling agent. 4.The highly dielectric film of claim 3, wherein the coupling agent is atitanium coupling agent or a silane coupling agent.
 5. The highlydielectric film of claim 1, comprising a coupling agent.
 6. The highlydielectric film of claim 1, wherein the affinity improving agent is anepoxy group-containing compound.
 7. The highly dielectric film of claim6, wherein the epoxy group-containing compound is a compound representedby the formula (C3):

where R is hydrogen atom, a monovalent hydrocarbon group having 1 to 10carbon atoms which may have oxygen atom, nitrogen atom or carbon-carbondouble bond, or an aromatic ring which may have a substituent; l is 0 or1; m is 0 or 1; n is 0 or an integer of 1 to
 10. 8. The highlydielectric film of claim 1, comprising barium titanate oxide particles.9. The highly dielectric film of any of claim 1, which is a film for afilm condenser.
 10. A coating composition for forming a highlydielectric film comprising: (A) a vinylidene fluoride polymer, (B)barium titanate oxide particles and/or lead zirconium titanate oxideparticles, (C) an affinity improving agent comprising at least one kindof a coupling agent, a surfactant or an epoxy group-containing compound,and (D) a solvent, wherein said barium titanate oxide particles and/orlead zirconium titanate oxide particles (B) and said affinity improvingagent (C) are contained in amounts of 10 to 500 parts by mass and 0.01to 30 parts by mass, respectively based on 100 parts by mass of thevinylidene fluoride polymer (A).
 11. The coating composition of claim10, wherein the affinity improving agent (C) is a coupling agent and/ora surfactant.
 12. The coating composition of claim 11, wherein thecoupling agent is a titanium coupling agent, a silane coupling agent, azirconium coupling agent or a zircoaluminate coupling agent.
 13. Thecoating composition of claim 12, wherein the coupling agent is atitanium coupling agent or a silane coupling agent.
 14. The coatingcomposition of claim 10, wherein the affinity improving agent is anepoxy group-containing compound.
 15. The coating composition of claim14, wherein the epoxy group-containing compound is a compoundrepresented by the formula (C3):

where R is hydrogen atom, a monovalent hydrocarbon group having 1 to 10carbon atoms which may have oxygen atom, nitrogen atom or carbon-carbondouble bond, or an aromatic ring which may have a substituent; l is 0 or1; m is 0 or 1; n is 0 or an integer of 1 to
 10. 16. The coatingcomposition of claim 10, comprising barium titanate oxide particles. 17.The coating composition of claim 10, which is used for forming a highlydielectric film for a film condenser.
 18. A method of producing a highlydielectric film, said highly dielectric film comprising: (A) avinylidene fluoride polymer, (B) barium titanate oxide particles and/orlead zirconium titanate oxide particles, and (C) an affinity improvingagent comprising at least one kind of a coupling agent, a surfactant oran epoxy group-containing compound, wherein said barium titanate oxideparticles and/or lead zirconium titanate oxide particles (B) and saidaffinity improving agent (C) are contained in amounts of 10 to 500 partsby mass and 0.01 to 30 parts by mass, respectively based on 100 parts bymass of the vinylidene fluoride polymer (A), characterized by subjectingthe coating composition of claim 10 to coating on a substrate anddrying.